1. Field of the Invention
The invention relates to fixed-ratio traction roller transmissions in which the contact forces applied to the traction surfaces, which are in contact with one another for the transmission of movement, are dependent on the torque transmitted through the transmission.
2. Description of the Prior Art
Traction roller transmissions require large contact forces for the frictional engagement of their motion transmitting rollers in order to prevent slippage. However, the required contact forces vary with the amount of torque transmitted through the transmission. In the "Mechanical Design And Systems" handbook, pages 14-8 and 14-9, McGraw-Hill, New York, 1964, a planetary type traction roller transmission is described in which, in the simple arrangement of FIGS. 14.6 and 14.7, the outer ring surrounding the sun and the planetary rollers is slightly undersized so as to compress and force the traction rollers and the sun into frictional engagement with each other. With this arrangement however, the pressure on the traction surfaces is always the same, that is, it is always high independently of the torque transmitted through the transmission.
There are also traction roller transmissions in which the contact forces applied to the traction rollers are variable and depend on the torque transmitted through the transmission. Applicants earlier, U.S. Pat. No. 4,052,915, for example, has a number of traction rollers disposed in an annular space formed between a sun roller and slightly conical traction rings so mounted in the transmission housing that a torque transmitted through the transmission forces the traction rings toward each other for engagement of the traction rollers with the ring and the sun roller.
In all these arrangements however, the sun roller and the ring rotate in opposite directions relative to the movement of the planetary roller axes and, accordingly, special provisions are required to maintain the planetary roller axes in exact parallel alignment with the axes of the traction rings and of the sun roller. Furthermore, as the traction ring will always rotate in a direction opposite to the direction of rotation of the sun roller assuming that the "planetary" rollers are only permitted to rotate about their own axes, an output shaft connected to the traction rings will always rotate in a direction opposite to that of an input shaft connected to the sun roller. Rotation of the input and output shafts in opposite directions however, is sometimes undesirable and the transmission support structure requires heavy mounts capable of assuming the full reaction torque of the output shaft.